The conventional GPS comprises 24 GPS satellites that are in 6 orbits and circle the earth approximately 12 hours at an altitude of about 20,200 km and at an inclination angle of 55 degrees. A GPS receiver on the earth receives navigational data necessary for position determination from 3 to 4 satellites of these 24 GPS satellites. The receiver then computes the location, the velocity, etc. of a vehicle or moving object carrying the receiver. The receiver can also find the velocity vector of the moving object by measuring the Doppler frequencies of the carrier waves. The GPS satellites use two transmission frequencies: L1 having a frequency of 1.57542 GHz and L2 having a frequency of 1.22760 GHz. L1 is used for normal determination of locations, and is PSK (phase shift keying)-modulated by pseudo-noise codes that are synthesized waves representing navigational data including C/A codes identifying satellites, information about the orbits of the satellites, and time information. The waves are caused to spread into a spectrum and transmitted from the satellites. These waves are received by the GPS receiver shown in FIG. 6. This receiver has an antenna 601 receiving signals of 1.57542 GHz. The signals are amplified by an L-band amplifier circuit 602. The output signal from this amplifier circuit 602 is converted into a first intermediate-frequency (IF) signal in the band of tens of MHz to 200 MHz by a down-converter portion 603 and then into a second IF signal in the band of approximately 2 MHz to 5 MHz. The second IF signal is applied to a voltage comparator 604 and converted into digital form with a clock frequency several times as high as the IF signal. The output from the voltage comparator 604 is diffuse spectral data. A C/A code-generating circuit 606 produces the same C/A codes, or pseudo-noise codes, as the satellites. A message-encoding means 605 inversely diffuses the C/A codes from the C/A code-generating circuit 606 into the digital output signal from the voltage comparator 604. This operation is performed for plural satellites. Normally, a position-calculating means 607 finds position-locating data from the navigational data from four satellites. As GPS receivers are miniaturized in this way, proposals have been made to use them to find the distance traveled or the velocity of the user when he or she runs or walks, as disclosed in Japanese Patent Laid-Open No. 118156/1994.
Where the prior art GPS receiver is used to measure the distance traveled by a human body or its velocity, various problems take place. Where the GPS receiver is installed on a vehicle, if it is in a tunnel, in a building, or in a valley between tall buildings, the measurement is difficult to perform. In such places, the navigational operation can be continued, using self-contained navigation such as map matching. However, in the case of a small-sized GPS receiver such as the hand-held type, it is difficult to incorporate map information in the form of a CD-ROM into the small-sized GPS receiver because of its size. Where the receiver is installed in a vehicle, the distance traveled and the speed can be obtained from instruments installed on the vehicle. In the hand-held-type, the distance traveled and speed themselves are found from GPS satellites and, therefore, if the satellites cannot be captured, no measurements can be performed. Also, in order to accurately find the distance traveled and speed, it is necessary to constantly perform the measuring operation. This increases the amount of electric power consumed by the GPS receiver.